Light diffusers adopted in an ordinary large-scale display (e.g. rear projection screen and large-scale liquid crystal display) are commonly located at the outmost layer of the screen, thereby enabling the light emitted with good output brightness and wide-angle uniformity.
FIG. 1 shows the photometric performance pertaining to various kinds of similar products available in the current market. Curve A in FIG. 1 represents the photometric performance of the light diffuser disclosed in U.S. Pat. No. 6,327,083, “REAR PROJECTION SCREEN WITH REDUCED SPECKLE”, curves B and C respectively represents the photometric performance of two different conventional light diffusers, and curve D represents the photometric performance of a rear projection light diffuser. As seen in FIG. 1 that the foregoing diffuser can only provide a good photometric performance within the 60° front viewing angle at the audience side of the projection screen, whereas the brightness outside the 60° front viewing angle is considerably reduced. Consequently, the viewer sitting in front of the screen would experience a great brightness disparity when his viewing cover wide side angles. Therefore, the large-scale display screen fabricated by the prior art technique is unable to deliver a uniform illuminance required by the wide-angle viewing.
In addition, for those light diffusers fabricated by the prior art techniques, thick structure of approximately 1 mm is normally needed to boost the light diffusion efficiency when they are used in the large-scale display screen. The design as such would either reduce the brightness output or fail to meet the aforementioned requirement for wide-angle viewing. If the thickness of the light diffusing sheet member can be made thinner, said element can be used in the modern rear projection module.
FIG. 2 represents a schematic drawing of the diffuser disclosed in the U.S. Pat. No. 6,327,083. As seen in FIG. 1, the diffuser 40 is made up of a front lenticular lens array 40a having unique microstructure design, a bulk region 48, and a clear region 49. The lenticular lens array 40a is composed of a plurality of concave elements 42 and convex elements 44 aligned orderly, wherein the concave element 42 is filled with light diffusing particles 46. Closed examination at the structure of convex element reveals a depression of concave shape 441 and a wavy contour of varying flatness. The drawback of aforementioned invention is that the lenticules array 40a designed as such would require fabrication technologies involving semiconductor manufacturing and various sophisticated mechanical processing techniques, thus resulting in poor manufacturability and high manufacturing cost. Furthermore, despite having the advantage of being able to reduce the speckle patterns, as is claimed in this prior art, the aforementioned diffusion means is incapable of emitting light with superior brightness and good wide-angle uniformity.